Until recently, there have been two methods for connecting a network communication terminal such as a personal computer, to a network such as the Internet: dial-up IP (Internet Protocol) connection and leased line IP constant-connection.
The dial-up IP connection is a method, in which an IP address is temporarily borrowed by dialing into the computer of a business (provider) offering network connection service and thereby an individual network communication terminal is connected to a network with the IP address, which is mainly used by personal users.
The leased line IP constant-connection is a method in which a network communication terminal is constantly connected through a leased line to an IP network owned by a provider whereby the network communication terminal is connected to the IP network or the Internet network via the IP network, using an individual and fixed IP address granted by the provider. This method has been utilized chiefly by businesses.
In recent years, with an increasing number of businesses which uses the Internet for communication with their branches and affiliated companies, the number of contracts with providers for this leased line IP connection has increased. Moreover, nowadays more individuals enjoy the IP constant-connection through leased lines thanks to the lowering prices of network facilities such as access lines and routers.
Accordingly, businesses and individuals can have their network communication terminals constantly connected to IP networks or the Internet for use by making a contract with providers for leased line IP connection.
There are two modes of charging fees for such leased line IP constant-connection: a flat rate system in which a fixed fee is paid to a provider regardless of how much network connection service is used, and a meter rate system in which a fee is paid to a provider in accordance with how much network connection service is used.
In the case of charging for leased line IP constant-connection, a provider actually charges only for the amount of use of their IP network by a network communication terminal under contract.
FIG. 17 illustrates an example of the configuration of a network connection system 2 run by the above provider 1. In this network connection system 2 the Internet 5 is connected with a leased line 4 to an IP network 3 owned by the provider 1.
Also, a plurality of edge routers 61-6n are connected to the IP network 3, and each of the edge routers 61-6n is connected with wired or wireless leased lines 711-71n, . . . , 7n1-7nn to corresponding routers 911-91n, . . . , 9n1-9nn of users 811-81n, . . . , 8n1-8nn each granted a personal and fixed IP address by making a contract with the provider 1 for leased line IP connection.
Furthermore, each router 911-91n, . . . , 9n1-9nn is connected to a network communication terminal 1111-111n, . . . , 11n1-11nn such as a personal computer, with a communication line 1011-101n, . . . , 10n1-10nn such as an in-house LAN, for example, of each user 811-81n, . . . , 8n1-8nn.
Thereby, in the network connection service system 2 it is designed such that each user 811-81n, . . . , 8n1-8nn can connect his own network communication terminal 1111-111n, . . . , 11n1-11nn to the IP network 3 or the Internet 5 via the router 911-91n, . . . , 9n1-9nn, the leased line 711-71n, . . . , 7n1-7nn, and the edge router 61-6n, using the IP address granted by the provider 1, for communication with other users 811-81n, . . . , 8n1-8nnand for a variety of other purposes.
Also, the provider 1 is equipped with an charging center 12 which charges each user 811-81n, . . . , 8n1-8nn a meter-rate fee for such communication. When a network communication terminal 1111-111n, . . . , 11n1-11nn subject to charging communicates with another network communication terminal 1111-111n, . . . , 11n1-11nn, the charging center 12 is designed to be capable of charging the user 811-81n, . . . , 8n1-8nn by amount of communication or amount of communication time of a flow (a series of packets) passing through the edge routers 61-6n connected with the network communication terminals 1111-111n, 11n1-11nn subject to charging.
In practice, in the charging center 12, when charging is made in accordance with the communication amount of a flow, a meter rate fee for the flow passing through an edge router 61-6n is charged to the users 811-81n, . . . , 8n1-8nn having a source IP address and a sink IP address based on the source IP address and the sink IP address included in the flow.
Then, in the case where communication is made between a user 811-81n, . . . , 8n1-8nn having a contract with the provider 1 having the charging center 12 and a user 13 having a contract with another provider, the charging center 12 makes no-charge with respect to a source IP address and a sink IP address of the user 13 because no contract is made between the user 13 and the provider 1.
Also, since the charging center 12 is designed to perform charging based on each of a source IP address and a sink IP address, if the flow is sent by such user 13, no charging is made to the user 13 (with respect to the source IP address), but charging is certainly made to the user 811-81n, . . . , 8n1-8nn (with respect to the sink IP address). On the other hand, when a flow is sent to the user 13, no charging is made to the user 13 (with respect to the sink IP address), but charging is surely made to the user 811-81n, . . . , 8n1-8nn (with respect to the source IP address).
In this manner, in the network connection service system 2, charging is made with respect to each of a source IP address and a sink IP address, thus avoiding missing charging to contracted users 811-81n, . . . , 8n1-8nn.
In such a conventional network connection service system 2, however, in the case where a user 811-81n, . . . , 8n1-8nn communicates with a user 13 having a contract with another provider, as described above, since the charging center 12 charges a meter rate for a flow of communication only to the user 811-81n, . . . , 8n1-8nn having a contract with its own provider 1, the same meter rate fee is charged to the user 811-81n, . . . , 8n1-8nn regardless of whether the other user 13 as a communication partner is abroad, which has posed a problem that it is hard to provide service offering a lower rate if a communication partner is in the same country and a higher rate if a communication partner is in another country, as practiced in the telephone service for example.
Also, in a conventional network connection service system 2, in such a case that a network communication terminal 13A of a user 13 having a contract with another provider performs one-way transmission of flows with a malign intention, to a network communication terminal 1111-111n, . . . , 11n1-11nn, via the Internet 5, the IP network 3, and an edge routers 61-6n in succession, charging is made for these flows because the flows pass through an edge router 61-6n, which has caused a problem that charging is made to the user 811-81n, . . . , 8n1-8nn for such communication even though the user 811-81n, . . . , 8n1-8nn does not want to communicate with the network communication terminal 13A.
Further, in the network connection service system 2, even if the user 811-81n, . . . , 8n1-8nn uses a fire wall to reject malignant access from such network communication terminal 13A and thereby to destroy the flows by the access, the flows have passed through the edge router 61-6n connected to the user 811-81n, . . . , 8n1-8nn, so charging is made due to this information. Consequently, there still remains a problem that charging is made to the user 811-81n, . . . , 8n1-8nn for the unwanted communication even though the user 811-81n, . . . , 8n1-8nn does not want to communicate with the network communication terminal 13A.
Still further, in the conventional network connection service system 2, in the case where two users 811-81n, . . . , 8n1-8nn each having a contract with the same provider 1 communicate with each other, because flows exchanged between the two users 811-81n, . . . , 8n1-8nn pass through a first edge router 61-6n connected to one user 811-81n, . . . , 8n1-8nn and a second edge router 61-6n connected to the other user 811-81n, . . . , 8n1-8nn, charging is to be made to both users 811-81n, . . . , 8n1-8nn based on the flows passing through the first edge router 61-6n, and yet charging is again made to both users 811-81n, . . . , 8n1-8nn based on the flows passing through the second edge router 61-6n, which has caused a problem that charging is made twice to both users 811-81n, . . . , 8n1-8nn for the same flow passing through the IP network 3 (this is referred to as “double charging” hereinafter).